Figure out how to ignore build constants

[jkleiber]

Summary

BuildConstants.java should never have been checked into main in the first place, and its continued existence guarantees merge conflicts each time a new PR merges. Removing this file isn't straightforward because spotless may not handle it nicely

Work Scope

• Un check-in the BuildConstants.java file and gitignore it
• Try to make spotless happy (maybe just need to force merge for a blank slate)